1. Field of the Invention
The present invention is directed to aqueous gel ink-filled ball point pens, more specifically to ball point pens having a ball of a diameter of 0.6 mm to 2.0 mm, and filled with an ink containing a special colorant whose specific gravity is 2 or more and has properties expressed by pseudo-plasticity, non-Newtonian viscosity or shear thinning viscosity.
2. Description of the Prior Art
A ball point pen is composed of a pen tip comprising a ball and a tip holder, an ink reservoir and a barrel. In writing with a ball point pen, the ink flowing out of the inside of the tip with rotation of the ball is transferred on or penetrated into a recording material such as paper, whereby letters and lines are written.
One advantage of aqueous ink-filled ball point pens is that the pens use inks having a low viscosity of several mPa""s, and therefore can write at a low writing pressure and impart a good writing feeling. However, one defect of aqueous ink-filled ball point pens is a natural outflow of the ink from the point of the tip, a so-called xe2x80x9cpoint seepagexe2x80x9d (hereinafter called a direct flow phenomenon) or a back-leaking phenomenon in which air flows in from the tip of the ball point pen to allow the ink to flow out from the ink reservoir. Ink absorbers comprising a bundle of fibers are used to prevent these phenomena.
Another problem with aqueous gel ink-filled ball point pens is that if the ball point pen is left in a cap-off condition, the solvent is dried up because of the high vapor pressure of the solvent, and therefore the pen point is dried to prevent the ink from flowing out. As a result, the ball point pen becomes incapable of writing.
On the other hand, a conventionally known oil based ink-filled ball point pen uses an ink having a high viscosity of several thousand mPa""s and therefore has the defect that the ball receives large resistance in rotating when the ink flow out of the pen tip, resulting in an unfavorable writing feeling. Further, if less amount of ink flows out of the tip in writing there is a blobbing phenomenon, unevenness on drawn lines, weak line intensity, and a high writing pressure is required.
One method of improving oil based ink-filled ball point pen, is to use a ball point pen for an aqueous ink having a so-called medium viscosity, which falls within a middle viscosity region (several mPa""s to several thousand mPa""s) ranging between the viscosities of an aqueous ink and an oil based ink. This is a ball point pen using a relatively low viscosity aqueous ink having the characteristic that the viscosity of the ink is lowered by the rotation of the ball point to allow the ink to flow out smoothly, a so-called shear thinning viscosity.
Inks of this type are known as xe2x80x9cgel inksxe2x80x9d, and the property thereof is shown by expression such as pseudo-plasticity, non-Newtonian viscosity and the like. However, if the ink has too strong a gel property, pigments in the ink coagulate and the flowability of the ink becomes inferior, so that outflow of the ink from the pen point is deteriorated in writing, and starving and inferior writing result. On the other hand, if gelation is weak and the viscosity is low, pigments in the ink are likely to be settled and that the ink is liable to bring about back flow or direct flow.
Further, with gel inks there is a possibility that a special pigment whose specific gravity is large can be used, although such a special pigment was not able to be used for conventional low-viscosity water based inks for a ball point pen. However, the strength of gel has to be increased when a pigment having a large specific gravity is used. Accordingly, at present, ink stability, writing feeling, back flow and direct flow phenomena, and pen structure exert influence on each other, so that an ideal aqueous gel ink-filled ball point pen has not yet been obtained.
An object of the present invention is to solve the problems described above and provide a ball point pen having less blobbing and capable of drawing stable lines having vivid color and no uneven intensity, wherein the ball point is filled with an ink using a pigment having a large specific gravity.
Intensive research by the present inventors has resulted in the finding that the problems can be solved by adjusting the relation of the structure of a tip with the strength of gel, and controlling the lay down value of ink, thus coming to complete the aqueous gel ink-filled ball point pen of the present invention.
The aqueous gel ink-filled ball point pen of the present invention is an ordinary ball point pen having a refill comprising a pen tip comprising a ball and a tip holder, an ink reservoir and a coupling for connecting the tip with the reservoir. The lay down value of the ink according to JIS standard S6053 is controlled to 220 to 800 mg/100 m, preferably 220 to 780 mg/100 m, by selecting an ink having a suitable viscosity ratio depending on the diameter of the point of the tip or selecting a suitable tip depending on the viscosity ratio of the gel ink.
That is, the aqueous gel ink-filled ball point pen of the present invention is different from ones obtained by merely charging conventional ball point pens with a conventional gel ink, in which the colorant is a pigment whose specific gravity is small.